1. Field of the Invention
The present invention relates to stepping motors for controlling an exhaust-gas-returning valve in an exhaust gas re-circulation system attached to an internal combustion engine, and in particular relates to a malfunction-detecting device for an EGR stepping motor, which detects the malfunction of the stepping motor.
2. Description of the Related Art
Hitherto, as pollution control in automobile exhaust gas, an exhaust gas re-circulation (EGR) system is known for reducing nitrogen oxides (NOx) in exhaust gas of an internal combustion engine. In the EGR system, a part of exhaust gas is returned from an exhaust gas passage to an intake passage via an exhaust gas returning passage connecting the exhaust gas passage to the intake passage of the internal combustion engine so as to be re-circulated in fuel mixture to be sucked into the engine, so that the heat due to the combustion in the engine cylinder is absorbed by the inert gas in the exhaust gas so as to reduce the maximum combustion temperature, thereby reducing NOx.
However, the re-circulation of exhaust gas causes reduction in the output of the engine and instability in combustion, resulting in problems of deteriorated operationality and increased hydrocarbons (HC). Therefore, the re-circulating amount of the exhaust gas must be suitably controlled according to operational conditions so as to reduce the problems. For that purpose, an exhaust gas returning valve (EGR valve) is provided in an exhaust gas returning passage and the amount of the valve opening (opening area) is controlled. The EGR valve is conventionally controlled by using a stepping motor (EGR stepping motor) in general, because in the EGR stepping motor, digital control of closed loop can be performed; positional control is excellent; accumulated errors are small. A valve opening adjusting structure in that a valve disc is ascended or descended by the rotation of the stepping motor rotor is known.
FIG. 7 is a schematic illustration showing an overall structure of a commonly used internal combustion engine. In FIG. 7, an air flow sensor (AFS) 2 measures the amount of air sucked into an engine 1 which is an internal combustion engine; a throttle valve 3 adjusts the amount of air sucked into the engine 1 by operation linked to an accelerator pedal (not shown) which is generally operated by a driver; a throttle valve opening sensor 4 detects the position of the throttle valve 3; a clank angel sensor 5 detects the rotational speed and the position of a clank shaft of the engine 1; a water temperature sensor 6 detects the temperature of cooling water 1a as means for detecting warming up conditions of the engine 1; an O2 sensor 7 detects the concentration of oxygen in the exhaust gas exhausted from the engine 1; and a cylinder identifying sensor 13 identifies a combustion cylinder attached to a cam shaft.
An engine controller 8 determines operational conditions of the engine by receiving information from the above-mentioned various sensors arranged in each position of the engine 1 and performs the computation of various controlled variables according to the operational conditions, thereby burn fuel in a desired air-fuel ratio. An air by-pass valve 10 controls an air reservoir by-passing the throttle valve 3 and performs the rotational speed control of the engine during the idling when the throttle valve 3 is perfectly closed and the torque control during the running. An injector 11 supplies fuel to the engine 1.
An exhaust gas returning passage 23 is the EGR system for returning the exhaust gas exhausted from the engine 1 again to a combustion chamber in the engine 1 so as to burn it again by connecting an exhaust gas passage 22 to an intake passage 21. An EGR valve 12 is arranged in the exhaust gas returning passage 23 for controlling the amount of the EGR to be burnt again. A sparking plug 9, the air by-pass valve 10, the injector 11, and the EGR valve 12 are controlled by the engine controller 8.
FIG. 8 is a sectional view showing an example of an EGR valve structure. As shown in the drawing, the EGR valve 12 comprises a stepping motor 12a and a valve disc 12b. The stepping motor 12a comprises a stator 121 and a rotor 122 while the valve disc 12b comprises a valve 123 and a rod 124 having the valve 123 at one end affixed thereto and being vertically movable when viewed in the drawing. The exhaust gas flows into an entrance port 125 from the exhaust gas passage 22 and flows out of an exit port 126 toward the intake passage 21. These ports 125 and 126 form parts of the exhaust gas returning passage 23.
When the rotor 122 is rotated by a driving signal to the stepping motor 12a, the rotation is converted into rectilinear motion by a screw 127 to be transmitted to a motor shaft 128. At this time, when the rotation of the stepping motor 12a is the normal direction, the motor shaft 128 moves the rod 124 upwardly when viewed in the drawing against a spring force of a spring 129 so that the valve 123 is moved in the separating direction from a seat member 130, thereby opening the EGR valve. On the other hand, when the rotation is the reverse direction, the motor shaft 128 moves the rod 124 downwardly in corroboration of a spring force of the spring 129 so that the valve 123 is moved in the approaching direction toward the seat member 130, thereby closing the EGR valve.
FIG. 9 shows a schematic connection diagram of a conventional malfunction-detecting device for the EGR stepping motor disclosed in Japanese Unexamined Patent Application Publication No. 3-203599, for example. In FIG. 9, a microcomputer 80 corresponds to the engine controller 8; a motor driving circuit 81 drives the stepping motor 12a of the EGR valve 12. In a break detecting circuit 82, transistors Tr1 to Tr4 are driving and detecting breaks; grounding resistances R1 to R4 are grounding emitters of the transistors; excitation coils S1 to S4 are the stator 121 of the stepping motor 12a; numerals C1 to C4 denotes comparators; potential dividing resistors R5 and R6 are dividing a power supply voltage Vc; numerals 511 to 514 denote delay circuits; numerals 521 to 424 denote D type flip-flop circuits; and numeral 53 denotes an AND circuit.
In the circuit of the conventional malfunction-detecting device for the EGR stepping motor shown in FIG. 9, when driving signals (symmetrical square-waves) having four phases being 90xc2x0 out of phase with each other are supplied to each base of the transistors Tr1 to Tr4 from the motor driving circuit 81, as shown in FIG. 10, the transistors Tr1 to Tr4 are turned on during the base input signal is in the high (xe2x80x9cHxe2x80x9d) level while are turned off during the low (xe2x80x9cLxe2x80x9d) level. When the transistor Tr1 is turned on, the excitation coil S1 is electrically excited while a non-inversion input terminal of a comparator C1 is to be the high (xe2x80x9cHxe2x80x9d) level by a voltage drop due to the resistor R1. To the non-inversion input terminal of the comparator C1, a dividing voltage due to the potential dividing resistors R5 and R6 is applied; since the voltage generated in both ends of the resistor R1 by the current flowing through the resistor R1 is set to be higher than the dividing voltage, the output voltage of the comparator C1 is to be the high (xe2x80x9cHxe2x80x9d) level.
On the other hand, during the off of the transistor Tr1, the above-mentioned current does not pass through the excitation coil S1 and the resistor R1 so that the input voltage of the non-inversion input terminal of the comparator C1 is to be lower than the above-mentioned dividing voltage, thereby the output voltage of the comparator C1 is to be the low (xe2x80x9cLxe2x80x9d) level. As for the other transistors Tr2 to Tr4, the same operations are performed. The outputs of the comparators C1 to C4 are shown in FIG. 10 (broken lines show breaks).
The output voltages of the comparators C1 to C4 are applied to data input terminals of flip-flops 521 to 524; thereupon delayed for a predetermined time xe2x80x9cxcfx84xe2x80x9d by delay circuits 511 to 514; and latched at the time of inputting in the rising edge of the driving signals to be input to trigger terminals T1 to T4. Since the above-mentioned predetermined time xe2x80x9cxcfx84xe2x80x9d is set so that the rising edge positions of the input driving signals of the trigger terminals T1 to T4 are to be the high (xe2x80x9cHxe2x80x9d) level period of the input voltages (output voltage of the comparators C1 to C4) in the data input terminals of the D type flip-flops 521 to 524, all the output signals of each output terminal xe2x80x9cQxe2x80x9d of the D type flip-flops 521 to 524 are to be the high (xe2x80x9cHxe2x80x9d) level, in the normal period. Therefore, the high (xe2x80x9cHxe2x80x9d) level signal is normally extracted from an AND circuit 53.
When a break is assumed to be generated in the excitation coil S3, even when the driving signal of the high (xe2x80x9cHxe2x80x9d) level is supplied to the base of the transistor Tr3, the current, which has to pass through the collector of the transistor Tr3 via a resistor R7 and the excitation coil S3, does not flow therethrough so that the transistor Tr3 remains as off, thereby the output voltage of the comparator C3 is to be the low (xe2x80x9cLxe2x80x9d) level in the period of being originally the high (xe2x80x9cHxe2x80x9d) level as shown by broken lines in C3 in FIG. 10. Therefore, only the output signal of the D type flip-flop 523 in output signals of the D type flip-flops 521 to 524 is to be the low (xe2x80x9cLxe2x80x9d) level at the rising time t1 of the input driving signal T3, thereby the output signal of the AND circuit 53 in the low (xe2x80x9cLxe2x80x9d) level is input into the microcomputer 80 as a break detecting signal.
The conventional EGR malfunction-detecting device formed as mentioned above is complicated in the circuit structure, comprising comparators, delay circuits, D flip-flops, and the AND circuit. The malfunction-detecting is performed along with the operation of an internal combustion engine; the operational speed of the stepping motor is high during the operation of the internal combustion engine, so that when trying to obtain furthermore detailed information, only the presence of wire breaks, etc., in the excitation coil or the wiring of the stepping motor can be detected because of an extremely small pitch of the detected signal, thereby there has been a problem that the furthermore detailed information cannot be obtained.
In order to solve the above-mentioned problems, it is an object of the present invention to provide a malfunction-detecting device for an EGR stepping motor wherein a circuit structure is furthermore simple and also more detailed malfunction information can be obtained by detecting the malfunction of the stepping motor during initialization drive of the stepping motor when an engine is just started.
In view of the above-mentioned object, in accordance with the present invention, a malfunction-detecting device for an EGR stepping motor comprises a driving-signal monitoring circuit which monitors a voltage surge as a monitoring signal, wherein in order to determine the presence of wire breaks in excitation coils of the EGR stepping motor, the voltage surge is generated by turning off a switching element for driving each of the excitation coils so as to cause self induction in the excitation coil.
A malfunction-detecting device may further comprise malfunction detecting means of the EGR stepping motor for counting the number of monitoring inputs to the driving-signal monitoring circuit during initialization driving of the EGR stepping motor so as to determine the presence of wire breaks in the excitation coils when the number counted is less than the number of times the coils are driven.
Preferably, the malfunction detecting means of the EGR stepping motor determines the number of phases having wire breaks in the excitation coils by the number of counts of the monitoring inputs to the driving-signal monitoring circuit during the initialization driving.
Preferably, the malfunction detecting means of the EGR stepping motor comprises: initialization driving detecting means for detecting that an EGR valve is undergoing initialization driving; driving-pattern change detecting means for detecting a change in the driving pattern of the EGR valve; monitor input detecting means for detecting the monitor input from the driving-signal monitoring circuit; count addition means for adding one count for every monitor input while repeating the above-mentioned detection by the initialization driving detecting means, the driving-pattern change detecting means, and the monitor input detecting means until completion of the initialization; and malfunction state determining means for determining whether the excitation coils are normal and if not normal, the number of phases having wire breaks therein by classifying counted values in association with the number of phases of the stepping motor.
A malfunction-detecting device may further comprise malfunction detecting means of the EGR stepping motor for detecting wire breaks in the EGR stepping motor by recognizing that a monitor input of driving signals is not input in the preceding driving state when the EGR stepping motor is stopped after it was driven corresponding to operational conditions of an engine.
A malfunction-detecting device may further comprise: initialization-completion detecting means for detecting that initialization of an EGR valve has been completed; monitor input memorizing means for memorizing monitor input when the monitor input was generated by the driving of the EGR valve corresponding to operational conditions of an engine; driving-completion detecting means for detecting completion of driving of the EGR valve when it was driven; driving-stop detecting means for detecting a predetermined time elapsed after stopping of the EGR valve; monitor input detecting means for detecting whether monitor input is generated to the driving-signal monitoring circuit; and malfunction determining means for determining whether the excitation coils are normal or have wire breaks by examining the presence of the monitor input.